A major cause of economic losses in the U.S. swine industry is porcine reproductive and respiratory syndrome (PRRS) virus, or PRRSV. PRRSV is the causative agent of reproductive failure and respiratory disorders in pigs. The economic losses associated with PRRS are mainly due to its involvement in abortion in pregnant females and respiratory disease complex (PRDC) in growing pigs. Different control measures including the use of vaccine and management change have been practiced. See U.S. Pat. No. 5,690,940, for example. Despite routine vaccination, however, it is not uncommon for outbreaks of PRRSV to occur on swine farms.
The outbreaks are most commonly due to the failure of bio-security measures. Poor detection of PRRSV infected replacement gilts into herds has been a common source of bio-security failure. These problems may be prevented if a simple and inexpensive method to test for PRRSV infection was available on farms. Such a method may also be applied to testing whether sows are producing negative weaned pigs and during acclimatization procedures.
In order to test PRRSV antibody, veterinarians should collect blood samples and send them to a veterinary diagnostic laboratory. At present, ELISA, indirect fluorescent antibody test and immunoperoxidase monolayer assay are common laboratory methods to detect anti-PRRSV antibody. However, these methods require expensive equipment and trained laboratory techniques. Using these techniques, at least 3 days including mailing time are required to obtain a result. In addition, swine farmers have to incur costs for collecting samples and shipping them to a diagnostic laboratory. A field-based, simple and rapid test for the detection of PRRSV antibodies would be very useful in laboratories of veterinary clinics or corporate swine farms. Eradication of the disease using PRRSV vaccine has not been routinely successful at the farm level. Methods such as total depopulation and repopulation have shown to be effective for on-farm eradication. However, such methods cannot be used in every farm and is relatively expensive to perform.
Moreover, such methods are dependent upon detection of PRRSV. The nucleic acid sequences and encoded proteins of some PRRSV strains have been described. The detection of PRRSV via tissue samples, including lung tissue, has also been discussed (see WO 96/06619), which is consistent with the observation that PRRSV preferentially replicates in alveolar lung macrophages. After infection by the oronasal route, PRRSV replicated in lung macrophages proceed to the lung lymph nodes and then to different organs via blood stream.
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